Cutting tip for rotating cutting tool and rotating cutting tool using the tip, and method of machining using the tool

ABSTRACT

The present invention provides a cutting insert, a rotating cutting tool holding said cutting insert and a cutting method using the tool which is able to prevent the occurrence of burrs and to cut a smooth finished surface. 
     In a rotating cutting tool which carries a plurality of cutting inserts, at least one insert is made of single crystal diamond  3 A, and the minor cutting edge of the insert has an arc shaped portion whose radius is in the range of 10 mm or more to 500 mm or less. 
     A high hard material other than single crystal diamond, for example PCD  3 B, is used for the remainder of the cutting inserts. 
     It is preferable that a cutting edge of single crystal diamond  3 A be projected to the rotating axis direction in the range of 0.01 mm or more to 0.05 mm or less, compared with the cutting edges of high hard material.

TECHNICAL FIELD

The invention pertains to an insert for a rotating cutting tool, arotating cutting tool and cutting method using the rotating cutting toolthat provide improved performance features for non ferrous metals suchas aluminum cast alloys.

BACKGROUND ART

A sintered diamond body (PCD) tool has been widely used in cutting nonferrous metal, especially aluminum alloy for automotive parts andelectronics parts. For example as shown in FIG. 1 a face milling cutterhaving a ring shaped body 1 which holds a plurality of locating pieces,each locating piece carrying an insert 3 is well known. Almost all of aninsert 3 is composed of cemented carbide and PCD is only used at thecutting edge. All the cutting edges of the insert 3 are made of PCD.

A cutting edge of an insert has an ordinary wiping edge (the first minorcutting edge), and each insert is held by a means of uniform projectionto the rotating axis direction. When a high accurate finished surface isrequired, a face milling cutter in which some of the inserts areprojected to the rotating axes direction compared with other inserts isknown (Japanese Patent Laying-Open No. Tokukaihei 8-309612) At thattime, a wiping edge with a gentle arc cutting edge has often been used.

DISCLOSURE OF INVENTION

As described above, the rotating cutting tool holding inserts whosecutting edges are made of PCD has mainly been used for milling such asaluminum die casting alloy, because PCD possesses appropriate hardnessand toughness. In particular, a wiper insert with an arc shaped cuttingedge is often used to improve the bottom surface roughness in thefinishing machining process. When an arc shaped cutting edge is used,the unevenness of the finished surface decreases and smoothness of thesurface is improved. However since the contact length between awork-piece and a cutting edge increases, cutting resistance increasesand burrs tend to develop. The development of burrs causes an increasein the manufacturing process to remove the burrs and an increase in theproduction cost.

To inhibit the development of burrs, a sharp cutting edge is necessaryto improve the cut. Since PCD diamond is made by sintering diamondparticles with binder, it is impossible to make a cutting edge with acurvature that is smaller than the diameter of the diamond particles(about 5-20 μm). Therefore it is impossible to inhibit the developmentof burrs using PCD.

When cutting high ductile material such as an aluminum die castingalloy, a shape of a cutting edge is copied to the work-piece. Thereforesmall unevenness of the ridges at the cutting edge is required tomachine a smooth finished surface.

However since PCD is produced by sintering diamond particle with binder,diamond particles fall off from the PCD at the polishing cutting edge.Therefore the cutting edge of PCD decreases the smoothness of thefinished surface because the unevenness of the ridges at the cuttingedge inevitably is the same as the diameter of the diamond particle.

Therefore the object of the present invention is to provide such aninsert for a rotating cutting tool, a rotating cutting tool which holdsthe insert and cutting method as most effectively prohibiting thedevelopment of burrs and which forms a smooth finished surface on thework-piece.

The present invention accomplishes the above objects by using at leastone insert, among a plurality of inserts held by a rotating tool, havinga cutting edge with a defined shaped single crystal diamond.

A cutting edge which at least contributes to cutting is single crystaldiamond in this invented insert. A wiping edge provided at the cuttingedge has an arc shaped portion and radius of said arc being from 10 mmor more to 500 mm or less. Regarding a rotating cutting tool carrying aplurality of inserts, the invented tool uses at least one insert havinga cutting edge made of a single crystal diamond and having a defined arcshaped wiping edge. The characteristic of this invention is that thecutting edge of the remainding inserts are made of a high hard materialother than single diamond.

A large single crystal diamond is considered for use as a material for asharp cutting edge to prevent the occurrence of burrs. In a singlecrystal diamond, it is easy to form a sharp cutting edge (at a tip ofthe cutting edge) with sufficiently small curvature compared with PCD,because contrary to PCD, diamond particles do not fall out partiallyfrom a single crystal diamond. Also it is possible to form asufficiently smooth ridge at the cutting edge compared with PCD. Howevera single crystal diamond is a material which is liable to brittlefracture. On the other hand, a rotating cutting was generallyintermittent cutting, which impacted intermittently against a cuttingedge. Therefore, if a single crystal diamond was used as a cutting edgematerial for an insert in the prior rotating cutting tool, the insertcould not be used, because chipping occurred by impact at a cutting edgewhen metal material for structural use such as aluminum die castingalloy was cut. A single crystal diamond therefore was used for turning,which was continuous cutting and did not impact a cutting edge such asforming a lens made of ZnSe for a laser optical part. The applicationwas extremely limited in the cutting fields and also the cuttingcondition was limited to a very shallow depth of cut.

The present inventors have found that the occurrence of burrs could beprevented and the improvement of smoothness of the finished surface wereobtained provided that a definite arc shaped portion is formed at thecutting edge of the single crystal diamond. In particular, the presentinventors have found that using two kinds of inserts, one having saiddefined arc portion formed at the cutting edge of said single crystaldiamond and the other having a cutting edge made of high hard materialother than a single crystal diamond, has following advantages. Thecutting edge made of high hard material prevents excess intermittentimpact to the single crystal diamond, the invented cutting tool makes itpossible to prevent the occurrence of burrs and to obtain an extremelysmooth finished surface in milling aluminum alloy.

The present invention is explained in detail hereinafter.

Both a natural single crystal diamond and synthetic single crystaldiamond are available. A synthetic single crystal diamond is preferablesince synthetic diamond has small deviation in quality,well-proportioned shape, high strength and high heat conductivity. Inparticular, a diamond that includes a small amount of nitrogen and boronis preferable. For example, a I b type single crystal diamond includingnitrogen 20 wt. p.p.m. or more (Produced by Sumitomo Electric IndustriesLtd.: Registered Trademark: SUMI-CRYSTAL) and a II a type single crystaldiamond including nitrogen less than 20 wt. p.p.m. (Produced by SumitomoElectric Industries Ltd. Registered Trademark: SUMI-CRYSTAL TYPE II) areboth available.

When a single crystal diamond is used as a cutting edge which at leastcontributes to cutting, any direction is available, but the (110)surface is preferable because the surface direction has high chippingstrength.

Instead of using single diamond crystal, chemical vapor deposition (CVD)diamond which does not include binder is also available.

A cutting edge is constructed at an intersection line of the rake faceand flank face and is generally comprised of a major cutting edge, acorner such as a round corner and a chamfer corner, and a minor cuttingedge. An arrangement of these portions is shown in FIG. 8. FIG. 8 is anenlarged view of the cutting edge at an insert which is carried by arotating cutting tool such as a milling cutter. The milling cutterrotates around the center axes 6B and moves to feed direction 6A (toleft in the figure). The cutting edge which mainly cuts the work-piecefacing the 6A direction is called major cutting edge 4A, and the cuttingedge which mainly cuts finished surface 6 (milled bottom surface) iscalled minor cutting edge 4C. The major cutting edge 4A and minorcutting edge 4C are occasionally directly connected, generally howeverthere is a corner 4D between the main cutting edge 4A and minor cuttingedge 4C. Regarding the corner 4D, liner chamfer as shown in FIG. 8 andarc shaped round corner are available. The arc portion disclosed in thisinvention is provided at minor cutting edge 4C. This arc has a center4E, which is the 6B side from the major cutting edge 4A and radius 4Fabove the finished surface 6, and connects with the corner 4D. A minorcutting edge is formed into arc shaped, in other words, a wholly arcshaped minor cutting edge is preferable and a partially arc shaped minorcutting edge is also preferable.

The radius of the arc is in the range of 10 mm or more to 500 mm orless, preferably in the range of 200 mm or more to 500 mm or less. Whenthe radius is shorter than 10 mm, sharpness decreases and burrs form.Contrarily when the radius is over 500 mm, there is no difference in thelinear minor cutting edge, and it is difficult to improve the surfaceroughness of the finished surface.

It is preferable that the curvature of the ridge at the wiping edge isin the range of 0.1 μm or more to 3 μm or less. The curvature is definedas the radius of the cross section perpendicular to the ridge of thecutting edge, which is formed at the intersection line of the rake faceand flank face.

To obtain a finished surface with few burrs, a high quality cutting edgeis essential. However when PCD is used as the cutting edge, it isimpossible to form a curvature at a cutting edge smaller than the extentof the diamond particle (5-20 μm), because an included diamond particlefalls off as a particle unit. On the other hand, the cutting edge madeof a single crystal diamond provides higher performance than PCD becausea single crystal diamond does not have such drawbacks. The insert with acurvature smaller than 0.1 μm is too expensive and liable to chip,therefore the insert is unsuitable for a rotating cutting tool such as aface milling insert. On the other hand, when the curvature is too large,there is no advantage over the PCD. Therefore the curvature ispreferable in the range of 0.1 μm to 3 μm.

The unevenness of the ridge at a wiping edge is preferable in the rangeof 0.1 μm or more to 3 μm or less. The unevenness at the ridge of thewiping edge is the deference between the highest projected portion andlowest recessed portion at the wiping edge and the neighborhood aroundthe wiping edge which contributes to cutting.

In order to improve the smoothness on the work-piece, it is necessary todecrease the unevenness at the ridge of the wiping edge, because theshape of the ridge at a wiping edge is copied to a work-piece. It is toocostly to obtain unevenness at the ridge of a wiping edge smaller than0.1 μm, because precious machining is necessary. When the unevenness atthe ridge of the wiping edge is larger than 3 μm the unevennessdecreases the smoothness of the work-piece, because the wiping edge iscopied to the work-piece. Therefore the unevenness at the ridge of thewiping edge is preferable from 0.1 μm to 3 μm.

The rotating cutting tools include milling cutter (including end mill),drill and reamer. The insert can be used as an indexable insert, whichis carried by the body of said rotating cutting tool. It is especiallypreferable to use the insert as a face milling cutter which is used inthe field of easily forming burrs.

It is preferable that there are the fewest possible number of insertshaving cutting edge of single crystal diamond to decrease the productioncost. Despite there being few inserts having a cutting edge of singlecrystal diamond in a rotating cutting tool, the tool accomplishes theobject of the present invention that is, to prevent the occurrence ofburrs and to finish a smooth work-piece surface. A milling cutter usingindexable inserts generally carried 4 to 24 inserts. A milling cutter ofthe present invention uses 1 or 2 inserts of single crystal diamond as acutting edge among 4 to 24 inserts. For example, a milling cutter whichuses fewer than 10 inserts, held one insert having a cutting edge ofsingle crystal diamond. A milling cutter using more than 10 inserts heldtwo inserts having a cutting edge of single crystal diamond.

It is preferable that the rake angle of the axis direction is in therange of about 10 degrees to −20 degrees in the insert having a cuttingedge of a single crystal diamond. More preferably it is in the range ofabout 5 degrees to −10 degrees and most preferable at around 0 degree tomaintain the sharpness of the cutting edge. It is preferable that theflank angle is in the range of about 3 degrees to 5 degrees. These anglelimitations make it possible to enlarge an angle between the rake faceand flank face, and strengthen the cutting edge and repress the chippingof the inserts. When the cutting speed is high such as 5000 m/min. Therake face is preferably in the range of −5 degrees to −10 degrees toprevent chipping.

The meaning of the rake angle of the axis direction is not an angle ofthe insert itself but a practical rake angle of inserts carried in themilling cutter. It is preferable that a rake angle of the standaloneinsert have a negative angle and the practical rake angle be around 0degree.

A high hard material other than single crystal diamond means a cementedcarbide, a cermet, cubic boron nitride sintered body and diamondsintered body.

It is preferable that an insert made of high hard material have a rakeangle of axis direction within the range of about 8 degrees to 20degrees, flank angle within the range of 5 degrees to 10 degrees. Thesepreferable angles make it possible to achieve good sharpness of thecutting edge.

Preferably a cutting edge of single crystal diamond projects in therange of 0.01 mm or more to 0.05 mm or less in the direction of therotating axis. The surface which is cut by the minor cutting edge of ahigh hard material is then cut preciously by the minor cutting edge of asingle crystal diamond in this milling cutter (minor cutting edge iswiping edge). Therefore an extremely smooth surface is obtained and theoccurrence of burrs is prevented on the milled surface of thework-piece.

Furthermore, the cutting edge of high hard material projects more thanthe cutting edge of a single crystal diamond in the radius directionwhich is perpendicular to the rotating axis. Since the work-piece in thefeed direction is cut by the major cutting edge of a high hard materialand is not cut by the major cutting edge of a single crystal diamond inthis xmining cutter, chipping of the single crystal diamond isprevented. It is unnecessary to strictly define the extent of theprojection. The cutting edge of the high hard material projects so thatthe major cutting edge of a single crystal diamond does not contact thework-piece.

The present invented cutting tool is not limited to the material of thework-piece, but is suitable for cutting non-ferrous metals. The presentinvented cutting tool is available for aluminum alloy, high -silicon-aluminum alloy, Metal Matrix Composites (MMC), Fiber Reinforced Plastic(FRP), silicon crystal, germanium crystal and cooper, etc.

A cutting method using a single crystal diamond tool is characterized inthat its depth of cut is in the range of 0.01 mm or more to 0.05 mm orless. When the depth of cut is smaller than 0.01 mm, it is difficult tocut into a smooth finished surface, because of insufficient cuttingdepth. When the depth of cut is larger than 0.05 mm, chipping of thecutting edge is liable to occur. Generally the depth of cut means thedistance between the surface to be cut and the finished surface.Therefore the method defined by the depth of cut being in the range of0.01 or more to 0.05 mm or less applicable to the cutting tool havingone cutting edge. When the method is applied to the cutting tool havingmore than one cutting edge, all of the flat cutting edges shouldsubstantially project uniformly. As described hereafter, the inventedcutting tool has one or more cutting edges of single crystal diamond andcutting edge of high hard material, and the former cutting edges projectagainst the latter in the axis direction. It is preferable that theprojection length be in the range of 0.01 mm or more to 0.05 mm or lessand distance between surface to be cut and finished surface may be morethan 0.05 mm or more. It is essential in this invention that thepractical depth of cut which is cut only by the cutting edge of a singlecrystal diamond is in the range of 0.01 mm or more to 0.05 mm or less.

High cutting speed is preferable such as faster than 500 m/min,especially faster than 1000 m/min. Such high cutting speed decreasescutting resistance, and therefore maintains remarkable practical use.The upper limit of cutting speed is about 6000 m/min considering thedurability of the cutting edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a face milling cutter.

FIG. 2 shows an invented insert used for the milling cutter, FIG. 2(A)is a top view, FIG. 2(B) is a side view, FIG. 2(C) is a right side view,FIG. 2(D) is an enlarged view around a single crystal diamond.

FIG. 3 shows that a rotating locus of a single crystal diamond cuttingedge ties on a rotating locus of a PCD cutting edge.

FIG. 4(A) is a measurement result of the surface roughness obtained byExample 1, and FIG. 4(B) is a measurement result of surface roughnessobtained by comparative Example 2.

FIG. 5(A) is a microscopic photograph which shows the side view of awork-piece cut by a wiper insert of single crystal diamond, FIG. 5(B) isa microscopic photograph shows a side view of a work-piece cut by wiperinsert of PCD.

FIG. 6 is an enlarged photograph of a cutting edge of single crystaldiamond observed from the vertical direction to the rake face.

FIG. 7 shows the profile of a vertical cross section to the ridge of acutting edge made of a single crystal diamond.

FIG. 8 is an enlarged view of a wiping edge of an insert which is heldby a rotating cutting tool.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereunder, preferable embodiment of the invention is described.

FIG. 1 is a perspective view of an embodiment of a milling cutter of theinvention. This face milling cutter is composed of a ring shaped body 1which held plurality of locating pieces 2 made of steel and eachlocating case 2 fixes the cutting insert 3. The insert 3 is mainly madeof cemented carbide and the cutting edge only is made from differentmaterial. The cutting edge of one among 6 inserts is composed of asingle crystal diamond 3A, and the remainders of five inserts arecomposed of PCD 3B in FIG. 1.

FIG. 2 shows an invented insert, the cutting edge of which is composedof single crystal diamond. FIG. 2(A) is a top view of an inventedinsert, FIG. 2(B) is a side view seen from the upper side of FIG. 2(A),FIG. 2(C) is a side view seen from the right side of FIG. 2(A) and FIG.2(D) is an enlarged view of the cutting edge made of a single crystaldiamond 3A. The single crystal diamond 3A is united with the substrateof cemented carbide 3C as a cutting edge to form the insert 3. The firstminor cutting edge (wiping edge) 4C has an arc shaped portion which hasa center at the left side of the first minor cutting edge 4C in FIG.2(D) and a radius of 300 mm in insert 3. The arc portion provided at theminor cutting edge 4C and linear portion is tied together at 3D(Referring to FIG. 2(B) and FIG. 2(C)), which emerges at the polishingstep of the production. Step 3E is provided to adjust a single crystaldiamond 3A on the top surface of the cemented carbide substrate.

Further a rotating locus of single crystal diamond cutting edge lies ona rotating locus of polycrystalline diamond cutting edge in FIG. 3 forexplanation. The vertical direction is a rotating axis direction, andthe horizontal direction is a radius direction in FIG. 3 An arrow 6A inFIG. 3 shows the feed direction of the milling cutter.

The cutting edge of single crystal diamond (chain line) is composed ofmain cutting edge 4A, round corner 4B and wiping edge 4C (the firstminor cutting edge) to form a finished surface. The wiping edge is anarc shaped portion among these.

On the other hand, a cutting edge (solid line) of PCD comprises maincutting edge 5A, chamfer corner 5B and linear flat cutting edge 5C (thefirst minor cutting edge).

The wiping edge 4C of a single crystal diamond projects from the cuttingedge 5C of PCD in the rotating axis direction. The length of projectionV is from 0.01 mm to 0.05 mm. Therefore, the finished surface of thework-piece is cut by wiping edge 4C made of a single crystal diamond.The main cutting edge 5A made of PCD projects from the main cutting edge4A made of a single crystal diamond in the radius direction (feeddirection). The length of projection is 1 mm. Therefore the cutting inthe tool feed direction is carried out by the main cutting edge 5A madeof PCD, and main cutting edge 4A made of a single crystal diamond doesnot contribute.

Thus the PCD insert is used as the main cutting edge which mainlyproduces chips, and single crystal diamond which is suitable forprecision machining is used as the wiping edge which mainly cuts thefinished surface. The wiping edge makes it possible to prevent chippingand the occurrence of burrs, and therefore to form a super finishedsurface.

(Test 1)

The surface roughness of the finished surface, the existence ornonexistence of burrs and shiny were investigated by cutting using theinvented milling cutter and prior milling cutters. Here, three kinds ofmilling cutters of the following constructions are examined under thefollowing cutting condition.

-   (1) All of the inserts have a linear flat cutting edge of PCD.    (Comparative Example 1)-   (2) One PCD insert has an arc shaped (radius of 300 mm) wiping edge    of PCD, and the remaining five inserts have a linear flat cutting    edge of PCD (Comparative example 2).-   (3) One insert has an arc shaped wiping edge of single crystal    diamond and the remaining five inserts have a linear flat cutting    edge of PCD (Example 1).

A single crystal diamond insert which was used in this test was producedby the process described below.

-   (1) A single crystal diamond stone which was produced by ultra-high    pressure and temperature press, was cut parallel to the (110) face    of the crystal and was cut into a 1.2 mm thick thin plate using a    laser cutter. A cemented carbide substrate was made separately by    prior art methods.-   (2) In respect of the thin plate obtained in above (1), the two    surfaces (up and down surface) cut by laser were polished into super    finished surfaces and 1.0 mm thickness.-   (3) The thin plate having a super finished surface obtained    above (2) was brazed on the cemented carbide substrate at the    vicinity of the cutting edge.-   (4) The brazed single crystal diamond was polished and formed a    cutting edge.

FIG. 6 is an enlarged photograph of the cutting edge made of a singlecrystal diamond after the completion of the above process. The cuttingedge was observed from the vertical direction to the rake face in FIG.6, and the black upper portion is the cutting edge. Chipping is notfound at the cutting edge, and it is observed that unevenness at theridge of the cutting edge is at most 3 μm as shown in FIG. 6.

FIG. 7 shows the profile of the vertical cross section to the ridge ofthe cutting edge. In the curve of FIG. 7, the oblique line on the leftside ascending to the right is a rake face and the oblique line on theright side descending to right is a flank face and the arc at the centeris the ridge of the cutting edge. It was confirmed that the curvature is1 μm at the ridge of the cutting edge.

(Construction of Milling Cutter) Face milling cutter: Outer diameter is100 mm and having 6 inserts Rake angle of a wiper insert made of PCD orsingle crystal diamond in axis direction: 0 degrees Flank angle of awiper insert made of PCD or single crystal diamond: +3 degrees Rakeangle of PCD insert: +10 degrees Flank angle of PCD insert: +5 degreesSingle crystal diamond: Produced by Sumitomo Electric Industries, Ltd

SUMI-CRYSTAL (Registered Trademark) PCD; Diamond particles 90% by volumeBinder (Co) + inevitable impurities: Remainder Mean particle diameter ofdiamond: 5 μm

Length of projection to the rotating axis direction of wiping edge ofthe wiper insert: 0.05 mm

Curvature of wiper insert made of a single crystal diamond at the ridgeof the cutting edge: 1 μm

Unevenness of wiper insert made of a single crystal diamond at the ridgeof the cutting edge: 0.2 μm

The sintered diamond Produced by Sumitomo Electric Industries, Ltd.:Registered Trademark: SUMI-DIA DA 2200) was used as inserts in additionto the single crystal diamond in these tests. The insert number isSNEW1204ADFR-W (produced by Sumitomo Electric Industries, Ltd.).

(Cutting Condition)

Cutting speed: 1000 m/min

Feed: 0.05 mm/insert

Depth of cut: 0.2 mm

Material of work-piece: ADC12 (Aluminum die casting alloy containing 10%by weight Si)

Cutting type: Dry

The results of the test are shown in Table 1

TABLE 1 Surface Surface roughness Burr condition Comparative Six PCDinserts × Δ × Example 1 having linear flat Rz: 1.13 μm about not cuttingedges 0.05 mm shiny height Comparative Five PCD inserts ◯ × × Example 2having linear flat Rz: 0.48 μm about not cutting edges and  0.2 mm shinyPCD insert having height wiping edge Example 1 Five PCD inserts ⊚ ⊚ ⊚having linear flat RZ: 0.3 μm    0 mm shiny cutting edges and a heightsingle crystal diamond insert having wiping edge ⊚: excellent, ◯: good,Δ: moderate to poor, ×: poor

As clearly shown in the Table, the surface roughness of ComparativeExample 1 is the most rough and is not shiny at the finished surface,but burrs remain comparatively small. The surface roughness isconsiderably improved in Comparative Example 2 because the wiper insertwas used. Because a PCD was used as the wiper insert having an arcshaped wiping edge, however, sharpness decreased and large burrsremained. On the other hand, because Example 1 used a wiper insert madeof single crystal diamond, an extremely smooth and shiny super finishedsurface was obtained. Also burrs were not observed at all.

FIG. 4 shows the measurement results of the finished surface roughness.FIG. 4(A) is the surface roughness of Example 1 and FIG. 4(B) is thesurface roughness of Comparative Example 2. The finished surface ofExample 1 is clearly smoother than Comparative Example 2. Also the arcshape of the wiper insert was copied to the finished surface almost thesame as in example 1, showing that the cutting edge of single crystaldiamond has good sharpness.

The measurement results in FIG. 4 were carried out under the conditionof cut off value of 0.8 mm and measurement length of 2 mm. Ra in theFigure is arithmetic mean roughness defined in Japanese IndustrialStandard (JIS) Number 0601, Rmax is maximum height excluding swellheight, Rz is mean roughness of ten points defined in JIS 0601, Rt ismaximum roughness excluding swell height defined in JIS 0601. Thesurface roughness curve is enlarged fifty times in the horizontaldirection and ten thousand times in the vertical direction.

(Test 2)

The effects were examined using a wiper insert made of a trial singlecrystal diamond. The first, a work-piece of ADC 12 was cut by an insertof the above Comparative Example 2 in the same manner as test 1, and theside surface which is vertical to the first finished surface wasphotographed from the direction of the edge line of the cutting surface.A milling cutter was then prepared in which a wiper insert having asingle crystal diamond cutting edge and a valance insert having nocutting edge were held at the opposite side of the body. Part of thebalance insert only balanced with a wiper insert of a single crystaldiamond, and did not cut. The first finished surface was again cut bythis milling cutter under the condition of 0.05 mm depth of cut. Thesurface which is vertical to the obtained second finished surface wasphotographed from the direction of the edge line of the cutting surface,and the effects of using a wiper insert made of a single crystal diamondwas confirmed.

Both results are shown in FIG. 5. The side surface of the work-piece cutby a wiper insert of a single crystal diamond is shown in FIG. 5(A), andthe side surface of the work piece cut by Comparative Example 2 is shownin FIG. 5(B). The photographs are taken from the right top side surfacewith diagonal illumination on the side surface from above the finishedsurface. The lower ⅔ of the photographs are the work-piece and the upper⅓ are the space above the finished surface. The white portion at theboundary of the work-piece and the space of the finished surface, isburrs. The finished surface appears gray because the finished surfacereflects in different direction from the camera. The burrs appear whiteas shown in FIG. 5(B), because a part reflects at the uneven burrs,which reaches the camera directly. When comparing both photographs, itis clear that there are no burrs on the finished surface milled with thewiper insert made of single crystal diamond.

(Test 3)

Cutting tests were carried out in the same manner as test 1, changingthe radius of the arc shaped cutting edge in Example 1. Six inserts wereprepared with radii of 5, 10, 100, 300, 500, 1000 mm. Cutting speed was3000 m/min.

The finished surface had no burrs and had a super finished surface withno cloudiness, when using wiper inserts having radii of 10, 100, 300 and500 mm at the arc shaped portion. On the other hand, the finishedsurface had many burrs and was not shiny when using a wiper inserthaving a radius of 5 mm at the arc shaped portion. Also, when using awiper insert having a radius of 1000 mm, the finished surface had smallburrs, and was not shiny, which was far from a super finished surface.

(Test 4)

Cutting tests were carried out in the same manner as test 1, changingthe projection of the wiping edge of the wiper insert in the directionof the rotating axis. Three projection lengths of 0.005, 0.03 and 0.07mm were used. Cutting speed was 500 m/min.

Consequently, a good burr-free finished surface was obtained only when awork-piece was cut by the milling cutter having a projection of 0.03 mm.A super finished surface was not obtained using a milling cutter havinga projection of 0.005 mm, because of insufficient cutting depth by thesingle crystal diamond. A super finished surface was also not obtainedusing the milling cutter having a projection of 0.07 mm, becausechipping occurred at the cutting edge of the single crystal diamond.

(Test 5)

Cutting tests were carried out in the same manner as test 1, changingthe curvature of the cutting edge. Three curvatures of 0.05, 3 and 3.5μm were tested. It was confirmed that the insert having a curvature of0.1 μm to 3 μm did not chip easily, had high quality cutting and lowproduction costs.

(Test 6)

Cutting tests were carried out in the same manner as test 1, changingthe unevenness at the ridge of the cutting edge. Three kinds ofunevenness at the ridge of 0.05, 3 and 3.5 μm were tested. It wasconfirmed that the inserts having unevenness from 0.1 μm to 3 μm tendednot to decreases the smoothness of the finished surface and wereproduced at low cost.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention, the cutting edgeis made of single crystal diamond and has a specific arc shaped portionat the first minor cutting edge. The advantage of the results is thatthe occurrence of burrs can be prevented and a super finished surfaceachieved. Since a rotating cutting tool of the present invention usesboth cutting edges made of the above single crystal diamond and of highhard material other than single crystal diamond, the constructionprevents excess cutting force to the cutting edge of the single crystaldiamond at cutting, burrs occurrence and realization of super finishedsurface.

Since the depth of the cut is specified in the present cutting methodinvention, the depth prevents chipping of the cutting edge despite beingmade of brittle single crystal diamond.

In addition, the rotating cutting tool of the present invention has theadvantages of achieving a super finished surface and preventing theoccurrence of burrs in the cutting of precious such as an aluminumalloy. Therefore it is possible to omit the process of removing burrs.

1. A rotating cutting tool comprising: at least one insert having asingle crystal diamond cutting portion with cutting edges comprising: amajor cutting edge; and a minor cutting edge with a wiping edge havingan arc shaped portion, wherein said arc shaped portion has a radius ofcurvature between 10 mm or more and 500 mm or less; and a plurality ofinserts made of high hard material other than single crystal diamond,each of the high hard material inserts having a cutting edge, whereinsaid wiping edge projects in the range of 0.01 mm or more to 0.05 mm orless to a rotating axis direction compared with the cutting edges ofhigh hard material inserts.
 2. The rotating cutting tool according toclaim 1, wherein said arc shaped portion has a ridge with a radius ofcurvature between 0.1 μm or more and 3 μm or less.
 3. The rotatingcutting tool according to claim 1, wherein said arc shaped portion has aridge with a surface roughness between 0.1 μm or more and 3 μm or less.4. The rotating cutting tool according to claim 1 wherein the cuttingedge of the high hard material inserts projects further than that of theat least one single crystal diamond insert in the radial direction.
 5. Amilling method comprising: providing a rotating cutting tool comprising:at least one insert having a single crystal diamond cutting portion withcutting edges comprising: a major cutting edge; and a minor cutting edgewith a wiping edge having an arc shaped portion, wherein said arc shapedportion has a radius of curvature between 10 mm or more and 500 mm orless; and a plurality of inserts made of high hard material other thansingle crystal diamond, each of the high hard material inserts having acutting edge; and using the rotating cutting tool by cutting a materialwith the single crystal diamond cutting edge to a depth of substantially0.01 mm or more to 0.05 mm or less, said depth is cut only by thecutting edge of the single crystal diamond.
 6. The rotating cutting toolaccording to claim 1, wherein the insert further comprises a bodyportion, made of a material different from single crystal diamond,united with the cutting portion.
 7. The rotating cutting tool accordingto claim 6, wherein the body portion comprises a cemented carbide.